The present invention relates to a process for making liquid crystal polymer ("LCP") blends, especially to a process for making compatible LCP/PPO and LCP/PPS blends.
Many polymers exhibiting liquid crystalline properties are known in the art. However, these polymers generally tend to be incompatible with other polymers. When a compatible blend of an LCP and another polymer is desired, it is often necessary to add a small amount of another ingredient or compatibilizer to promote more thorough blending between the two polymers. The additional ingredient may work by promoting bond formation between diverse polymer molecules. However, a compatibilizer that is effective in one system may not be effective in others; a great deal depends upon the specific functionalities of the molecules.
An important driving force in seeking new polymer blends is cost-effectiveness. It is often desirable, for example, to discover new blends that have one or more desirable characteristics found in an expensive polymer, but cost less. This is usually accomplished by finding a suitable blend comprising the expensive polymer and a less expensive one.
Another reason for blending polymers is to create compositions that are better able to meet special needs than the polymers known in the art. Accordingly, it is sometimes desired to combine an LCP with another polymer having special characteristics in the hope of creating a blend exhibiting the desirable characteristics of both polymers. For example, polyphenylenesulfide ("PPS") has very good thermal stability and chemical resistance, potentially important characteristics for an LCP blend. Polyphenyleneoxide ("PPO") exhibits reasonable impact resistance. However, LCP's are generally incompatible with PPO or PPS. LCP/PPO and LCP/PPS blends tend to have large regions or domains of the individual polymers rather than fine, well-dispersed domains; the large domains tend to produce poor properties, e.g. films having poor tensile properties.
It is known that phenols may be directly esterified using a combination of boric acid and either sulfuric acid or polyphosphoric acid as a catalyst. This process is described by Lowrance in "Boric Acid-Catalyzed Esterification Of Phenols", Tetrahedron Letters, No. 37, pp. 3453-4 (1971). However, this process has not been applied to polymers.